An American said "yeah, no" to me and I did not know if that was a yes. It is a no. "No, yeah" is a yes. "Yeah, no, for sure" is a yes. "No, yeah, no" is a no. I wrote these down and showed them to him. He read the list. He said nothing for a while. Then he said, "That's all correct." Then he said, "How is that all correct?" I asked him to explain the rule. He tried. He tried for four minutes. He kept starting sentences and abandoning them. Then his wife walked in and he read her the list and she said, "Yeah, no, that's right." He pointed at her. He said, "She just did it." She said, "Did what?" I have shown this list to nineteen Americans. All nineteen agree it is correct. Zero can explain it. Three have said "that's kind of scary." One went quiet and then said, "How much of what I say is like this." All of it. Almost all of it.